I remember watching a cartoon or anime around 2010 on TV about a group of boys who have an underground bunker and use a blue crystal as a key to travel into another dimension.
I remember one of them always stays behind and the rest go into the dimension as golems or similar creatures to fight. One boy is definitely blonde and one has glasses.
As per my answer to 2000s(?) TV show with 4 kids as the 4 elements who fought baddies in another universe, I think this is one of the Gormiti shows.
From TVTropes:
An episodic series fron Marathon Studio [...] narrating the adventures of a group of young children with the duty of keeping the peace in the parallel universe of Gorm, once home to a mighty race of warriors. Not an insignificant task, indeed, since events on Gorm tend to have repercussions on the Earth itself... and the villains of the show, the people of the Volcano, seem to be intent on causing as much of a ruckus as possible!
By calling the power of the ancient warriors, siblings Toby and Nick and their friends Lucas and Jessica can transform in Lords of Nature, gifted with the powers of (respectively) Water, Earth, Forest and Air, and fight against the people of the Volcano and their leaders, Orrore Profondo (Deep Horror), Lavion and Magmion. Episodes mostly revolve around the four kids balancing their superhero duty with real life, school and everyday activities... with the interesting variation that, in every mission, one of them (apparently selected at random) has to stay behind, in order to manage his/her friends' powers and give them instructions.
The credits show the kids and their transformations, which do look like golems.
